Oil and gas operators often drill wells in formations that require treatment of the producing formation or gravel packing to ensure optimum production. In past installations, such treatment or gravel packing was not attempted until after a well liner was positioned and cemented in place. The liner and its cement seal served to isolate the producing formation, or pay zone, from other zones above the pay zone so that there was no cross-contamination or fluid and material loss during treatment or gravel packing.
Presently, the liner cementing and formation treatment or gravel packing are accomplished as separate steps, requiring multiple equipment runs into the well bore. First, the well bore is drilled to the point where the liner will be seated. The liner is lowered into position and cemented into place. After the cement has set, a second, smaller diameter drill string is used to drill beyond the cemented liner into the pay zone. The drill string is removed and a circulation system is lowered into the pay zone for treatment or gravel packing of the pay zone. This system is expensive and time-consuming because it requires multiple trips in and out of the hole and multiple drilling runs.
In some cases, a single hole can be drilled into the pay zone, and the liner and production strings lowered in a single trip. However, these situations only occur when there is no need to treat the formation or gravel pack the production string, and the production string can utilize large-opening slotted or perforated production casing. The liner can be cemented into position and the well brought on line without multiple trips in and out of the hole because there is little or no danger of formation contamination or debris plugging the production casing. When formation treatment or gravel packing is required, large-opening production casing cannot be used and this simpler, one-pass approach is unavailable due to the danger of formation damage or plugging the small openings in the production screens.
It is an object of this invention to allow a single drilling operation to complete the well bore into the pay zone when formation treatment or gravel packing is required.
It is a further object of this invention to allow simultaneous insertion of cementing apparatus and formation treatment or gravel packing apparatus into the well bore.
It is a further object of this invention to allow cementing operations without danger of contaminating or clogging either the formation or production equipment installed below the cementing apparatus.